Cancer remains a formidable disease with a high mortality rate in today's society. Indeed, cancer is second only to cardiovascular disease as a cause of death, killing one out of four people in developed countries.
Cancerous tumors commonly originate from normal cells which transform into malignant cells or tumors. The initial tumor growth may be slow and thus may be difficult to detect. The growth often becomes more aggressive and invasive with time, eventually spreading throughout the whole body and resulting in death.
Photodynamic therapy (PDT) is one of the methods for treating tumors. For review, see Dougherty, T. J. Photochem. Photobiol. 1993, 58, 895. At present, the most commonly used sensitizers for clinical PDT practices are Photofrin II, an enriched active fraction of hematoporphyrin derivatives, and disulfonated aluminum phthalocyanine. These compounds, once photoactivated, induce severe oxidative damage to the structure of lipids, proteins, and nucleic acids. Since many biologically active molecules, e.g., DNA, demonstrate higher affinity toward stereospecific ligands, it is therefore desirable to develop stereospecific PDT sensitizers to enhance cytotoxicity of such antitumor agents.